The ending of IV. In the end, you save everyone, even Baldur, and while the Medium can't just magic away the fertility problems the Empire is having and that may someday threaten Tharsis, the entire tone of the ending is "you know, if we just cooperate and pool our knowledge, we can probably find an answer". You then see the transformed, cosmopolitan, newly-multiracial Tharsis through the eyes of a new set of adventurers, and see that all your friends are okay (and are talking the player guild up), ending with "Whirlwind" (in his old getup and everything!) showing the new kids the ropes just like he did for you. All while this song is playing.
Also in IV, despite Wufan showing disdain for humans and Logre/Whirlwind "betraying" you, you can choose to forgive them by choosing the "wordlessly extend your hand" option. So moved by your kindness, they join you as a guest - and then can become permanent members of your guild later on!